As is well-known in the art, effective antiperspirant chemicals are almost without exception acidic materials and, in general, the greater their acidity the greater their effectiveness as antiperspirants. The acidity of such materials, particularly that of the most highly acidic and effective materials such as aluminum chloride, raises a number of problems, among which may be mentioned corrosion of processing equipment, irritation of the skin of the user, and reduction of the tensile strength of fabrics in clothes worn by the user. Moreover, although aluminum chloride would be the preferred antiperspirant material because of its high antiperspirant activity, the utility of this material is severely limited by the difficulty of handling it in the anhydrous state in which it combines with water with explosive violence releasing great quantities of heat. For this reason, it has not been possible to use anhydrous aluminum chloride itself in the formulation of antiperspirant products. Therefore, it has been necessary heretofore to employ only aqueous solutions of this highly desirable antiperspirant chemical. While attempts have been made to remove the water from aqueous solutions of aluminum chloride to provide a dry powder material, none has been successful previously. When high heat has been used for this purpose, the aluminum chloride has been changed chemically to form aluminum oxide which is relatively ineffective as an antiperspirant. Attempts to avoid such oxidation of the aluminum chloride by the use of low heat in the drying of aqueous solutions of the chemical have also failed since the products have not been free-flowing readily utilizable powders. Moreover, since aqueous aluminum chloride has a pH of about 0.8, it is so acidic that it causes very serious corrosion problems.
Aqueous solutions of aluminum chlorhydrate, another commonly used antiperspirant chemical, have a pH of about 4.3 and are, therefore, much less corrosive, but this material is also less effective as an antiperspirant. It is recognized, however, that the antiperspirant activity of aluminum chlorohydrate can be increased by decreasing the proportion of aluminum to chlorine in the composition. Therefore, aluminum chlorhydrate compositions containing varying ratios of aluminum to chlorine are commercially available. In these compositions, as the proportion of aluminum to chlorine decreases from the 2:1 ratio found in aluminum chlorhydrate to the 1:3 ratio found in pure aluminum chloride, the effectiveness of the material as an antiperspirant is increased. However, the acidity of the material also increases and consequently the products become more difficult to manufacture due to corrosion normally attendant to the processing of such acidic materials. Many other astringent chemicals and combinations of chemicals useful as antiperspirants are known to the prior art. Among these, one of the best is zirconium hydroxychloride. This material, which has a pH of 1 or less, is also extremely difficult to process because of its corrosive nature.
Due to the acidity of the foregoing and other effective antiperspirant chemicals, it has been proposed to mix these materials with less acidic chemicals to achieve antiperspirant compositions which are effective but less corrosive and irritating than the unblended zirconium and aluminum salts.